If you're sending or storing local dates and times, it may actually be better to use the local time (as ISO 8601 does) with the (Olson tz) name of the time zone it's in, instead of the time zone offset as in ISO 8601. This is more resilient against future time zone rule changes, at least that's what this article argues: http://fanf.livejournal.com/104586.html .